Let me offer a non-GNURadio solution. This can probably be replicated in GNURadio but I haven’t done it and so would need to look into how feasible it is to implement. You can use Wireshark and any WiFi NIC to capture packets. If you can put the NIC is promiscuous mode you can sequentially tune it to each channel and record any packets that occur. I was dwelling on each channel for 3 seconds and scanning all the 2.4 and 5 GHz channels.
In each captured packet is the channel number being used and the RSSI of the signal at each device. For some purposes this RSSI is useful. If you can further measure the RSSI at your USRP you have 2 measures of the signal and that could potentially be very useful.
I also looked at things like the number of access points and attached devices. This is useful because you can start to compare environments based on the network configuration of the access points and the number of people using their devices in the area.
What this method does not tell you is what is out there that is not WiFi. In some recent measurements I am seeing an increasing number of Bluetooth and Bluetooth Low Energy. Not a surprise.